Mixing circuit arrangement



5, 1952 A. VAN WEEL 2,582,726

j MIXING CIRCUIT ARRANGEMENT Filed July 2, 1946 LOCAL u oscuurol? v 5 k 6 0 5 Z .Za 5 I 2 r 7 fig. 4.

LOCAL OSCILLATOR 1' 7 /3,T/2 viii/' LOCAL OSCILLATOR 5 '5 I N V EN TOR. ADELBERT MN MEL AGENZI Patented Jan. 15, 1952 MIXIN G CIRCUIT ARRANGEMENT Adelbert van Weel, Eindlioven, Netherlands, as'

signor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application July 2, 1946, Serial No. 680,930 v In the Netherlands March 27, 1943 l Section 1, Public Law 690, August 8, 1946 Patent expires March 27, 1963 This invention relates to amixing circuit which is particularly suitable for short waves and in which the incoming oscillations are supplied in push-pull and the local oscillations in single phase arrangement to the input electrodes of two discharge systems (mixing systems). In the transmission of ultra-high frequencies this receiving method has the advantage of yielding a low input damping and a better signal-to-noise ratio.

A circuit of this kind exhibits the drawback, however, that the inputimpedance of the mixing systems, more particularly in receiving ultrashort waves, has only a small value, due to which the voltage having the frequency of the local oscillations and being set up between the input electrodes of each of these systems usually becomes too low. To supply as high as possible a voltage having this frequency to the input electrodes of the mixing systems the (single-phase) circuit, which is constituted by the impedances, pairwise connected in parallel, of the two halves of the push-pull circuit and the parallel-connected input impedances of the two discharge systems, jointly with the impedances common to the input circuits of the two systems is, ac cording to the invention, tuned to the frequency of the local oscillations.

In the present case the expression push-pull circuit is to be understood to mean the assembly of impedances available between two not directly interconnected input electrodes of the discharge systems, in which are flowing currents having the frequency of the incoming oscillations, the expression input circuit of a discharge system being understood to mean all the impedances available between the input electrodes of a discharge system and in which are circulat- 3 Claims. (01. 25c 20) ing currents associated with this system and having the frequency of the local oscillations.

In order that the invention may be clearly understood and readily carried into effect it will now be described more fully with. reference to the accompanying drawing, representing several embodiments thereof.

Fig. 1 represents a mixing circuit which forms part of a superheterodyne receiver for short waves, in which the local oscillations are supplied in single-phase and the incoming oscillations are fed in push-pull connection to the mixing systems I, I" through a tunable lecher-system. The oscillations captured by a dipole antenna 2', 2" are supplied to two conductors 3, 3" forming part of the said lecher-system, which by means of a short-circuit bridge 4 is tuned to I the mixing systems.

oscillations. The antenna 2, 2" is connected to the lecher-system 3', 3" in such a manner as to ensure optimum matching of the antenna to The expression optimum matching is to be understood an adaptation by which either a maximum signal-to-noise ratio or maximum amplification is obtained. The conductors 3, 3" are connected to the=anodes of the said mixing systems .I I consisting of two diodes incorporated in asingle discharge tube. The cathodes of the two mixing diodes are interconnected and their junction is connected to earth through the intermediary of a source of potential 0 in which the local oscillations are generated. Consequently, the incoming oscillations are supplied through the lecher-system in push-pull, whereas thelocal oscillations are fed, by means of so-called cathode-injection, in single-phase (in the same phase) tothe input electrodes of the two diodes I, l'-.'

With thiscircuit, as has-been statedabove,

it proves to be very difficult in practice-to obtain a suflicient voltage having the frequency of the local oscillations across the mixingsystems.

According to the invention this difficulty is solved by tuning the single-phase circuit, which in the case under view is constituted by the parallel-connected input impedances of the two discharge systems (indicated -in the drawing by the capacities 5', 5"), the pairwise parallelconnected impedances of the two halves of the push-pull circuit (in the present case the conductors 3', 3"), jointly with the impedances common to the input circuits of-both systems (in the present case the impedance of the conductors 3', 3" with respect to thesurroundings as well as the impedance ofthe local oscillator O),

to the frequency of the local oscillations.

Fig 2 represents an embodiment of the invention in which this tuning can be realized in a simple manner. To this end the lecher wires 3', 3" are lengthened by parts 6, 6" and the ends are connectedby an earthed short-circuit bridge I, the extension'bein given such a value (which may be effected by adjustmentof the short-circuit bridge I) that the single-phase cir-- cult is tuned to the frequency of the local 'oscillations. As a result thereof series-resonance in regard to the oscillator frequency occurs in the circuit constituted by the local oscillator O, the

parallel-connected input impedances '5', 5", they parallel-connected lecher lines 3', 3" and 6', 6" and the impedance of the said lines with respect to earth, as a result ofwhich the voltage having this frequency across the capacities 5, 5" and' so the voltage between anode and cathode of any of the diodes acquires a maximum value.

If desired; thelengtlr of the conductors '6, 6".

may be made shorterthan in the case illustrated or may be reduced even to zero by interposing an impedance, preferably a variable impedance, between the short-circuit bridge I andoearthl The desired resonance can be achieved by adjusting this impedance to a suitable value.

Fig. 3 represents an embodimentof the 'inventionin which this is reduced to practice, the lecher system 3, 3", 6', 6" being surrounded at the same time by shielding means. 8 of. which the end 9 remote from the mixing systems I,

I" is earthed. bridge I of the extended lecher-system is not connected directly to earth but through the intermediary of a variable condenser In, this condenser being so adjusted as to establish the. de-. sired resonance.

Fig.4 represents'an embodiment of the invenncessary to lengthen thev two lecher wires. by pfeces'fifffi" in thevarious examplesy instead thereof=-a single wire, for instance, which ap plies-"at themiddle of the -short-circuit bridge 4 may "be -sufilcient.

In, the" executional examples the locationwhere the-incoming oscillations are supplied to thepush-pull circuit (in the present case the junction of the-antenna and the lecher-system 3", 3"")'may also be chosen arbitrarily. In choosingrthis location it may be contemplated whether it is desirable either to prevent radiation of the local oscillationsor'to attain optimum adaptation, In-fact, when the antenna is not in apotential node-in regard to the local oscillations, the'local' oscillations are radiated and, moreover, a variation insize of "the antenna-impedancehas a reactive eifect on the frequency of the local oscillator. Often, however, it is also desired to'connect the antenna to the lecher system at such a point as to obtain optimum matching and consequently maximumamplification and a maximum signal-to-noise ratio respectively;

When'distributing, however; theassembly of In this case theshort-circuit- The aforesaid resonance can be'estabimpedances" constituting the single-phase circuit" in a suitable manner with respect to the antenna junctions-{radiation of'the local oscillations" by theantenna L can be entirely or substantially entirely avoided in-a-ll cases;

Fig: 5'- illi1strat'es,'by-way'of' example, how this variable impedance. H animpedance l2, which is preferably'alsovariable, being connected'between the mixing' systems I, l" and earth, in serieswith the local oscillator 0; if desired; these'imp'ances'may consist of lecher systems;

By a suitable adjustment of the impedance H itcan be achieved that the right halfof' the single-phase circuit, reckoned from the antenna junctions to earth, is tuned to the frequency'of In regard to the left half of: the singl'e phase circuit; also reckoned from the local oscillations.

Between the short circuit bridge 1 and earthisinterposed apreferably the antenna junctions onwards, the same can be achieved by adjustment of the impedance l2. As a result thereof the whole of the single-phase circuit is tuned to the frequencyof 'the local oscillations and, moreover, the antenna exhibits a minimum potential difierence (of the frequency of. the local oscillations) with respect to the surroundings and so radiates the local oscillations as little as possible and not at all when making use of no-loss impedances. In the aforesaid manner it is consequently feasible not only to prevent the radiation of the local oscillations but also tov match the antenna in an optimum way .to the. mixing systems.

As mixing systems use may be made not only of diodes, but'also of triodes, tetrodes and so on. Advantageously the two mixing systems may often be jointly incorporated in one discharge tube and, as the case may be, have one cathode in common.

What Iclaim is:

1. An electrical circuit arrangement for mixing a first wave and asecond wave, comprising the following elements in series circuit arrange-' ment andin the order named, a first impedance element. first and second mixing elements arranged in' parallel relationship, a second impedance element having distributed electrical con'stantsand being" coupled in push pull rela-- tionship to said mixing elements and a third impedance element, means coupled in series with said" impedance elements to apply said first wave in the same phasetosaidmixing elements,

. and means coupled to said" second impedance element-at a point of optimum-matching to ap-= ply said second" wave tofsaid mixing elements,- said, firstand third impedance elements being adjustable relative to eachother to time said series circuitito thefrequency of'saidfirst wave 'and to provide at said second impedance elementa point'which is'a' potential node'for said" first wave substantiallycoincident tosaid point of optimummatchingr 2. An electrical circuit arrangement for mixing'a' first waveand a second wave, comprising'the following elements in series circuit arrangement and-in the-order named; a first im' pedance element, first and" second mixing elements arranged in" parallel relationship; a .sec-

ond'wave to said mixin elements. said circuit means; said; first impedance element, said mixing elementsandthe portion of said secondimpedance element between-said mixing elements and said 'first*pointforming a first series circuit, the" remainder of said second impedance element and said" third impedance element forminga second series circuit, said firstand' third impedance elements being" adjustable relative 'toeach other to tune each of said first and second series circuits to thefrequency' of said first-waveand to provide at said second, impedance-element a second point which is a potential node for said' first wave substantially coincident tosaid first point.

3. An -electrica'l circuitarrangement for mix inga first-waveand a second wave,gcomprising" the following elements in series circuit arrangeintent and in the order named, a first impedance element, first and second mixing elements arranged in parallel relationship, a lecher-system having one end thereof coupled to said mixing elements in push-pull relationship and having a short-circuiting member for tuning said coupled end to the frequency of said second wave and a second impedance element, circuit means coupled in series with said impedance elements to apply said first wave to said mixing elements, and means coupled to said lecher-system at a point of optimum matching thereon to apply said second wave to said mixing elements, said circuit means, said first impedance element, said mixing elements and the portion of said lechersystem between said mixing elements and said point of optimum matching forming a first series circuit, the remainder of said lecher-system and said second impedance element forming a second series circuit, said first and second impedance elements being adjustable relative to each other to tune each of said first and second series circuits to the frequency of said first wave and to provide at said lecher-system a second point which is a potential node for said first wave substantially coincident to said point of optimum matching.

ADELBERT VAN WEEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,980,158 Hansell Nov. 6, 1934 2,106,776 Trevor Feb. 1, 1938 2,211,003 Conklin Aug. 13, 1940 2,260,844 Thomas Oct. 28, 1941 2,307,074 Pray Jan. 5, 943 2,326,801 Pray Aug. 17, 1943 2,382,693 Dallenbach Aug. 14, 1945 2,427,241 Hofweegen Sept. 9, 1947 2,479,537 Fyler Aug. 16, 1949 

